Thermal ink jet printers apply ink to a print medium by ejecting small droplets of ink from an array of nozzles located in the printhead of a printer cartridge. An array of thin-film resistors on an integrated circuit on the printhead selectively generates heat as current is passed through the resistors. The generated heat causes ink contained within an ink reservoir to boil and be ejected from the array of nozzles that is adjacent to the resistor array. A printer controller determines which resistors will be "fired" and the proper firing sequence so that the desired pattern is printed on the medium.
Many multicolor ink jet printers accommodate replaceable ink cartridges containing multiple colors of ink as well as replaceable cartridges containing a single color of ink. The printer controllers of these printers require input of information identifying the type of cartridge that is installed so that the controllers are adjusted for proper printer operation with the installed cartridge. User interface is typically required to identify to the printer controller the type of cartridge installed.
In order to reduce the cost and complexity of printer cartridge manufacturing processes, it is desirable for all cartridges to be constructed with a similar configuration to the extent possible regardless of the type of cartridge or color of ink it contains. Thus it is desirable to maintain uniformity of cartridge configurations at least until the time that the cartridges are loaded with ink which typically occurs near the completion of the cartridge assembly process. However, maintaining a uniform cartridge configuration makes it difficult to easily identify the contents of the cartridge or the particular cartridge being used.
An object of the invention is to provide a relatively simple and inexpensive apparatus for encoding information on a printer cartridge.
Another object of the invention is to provide cartridge-specific information, such as ink color and type, on the cartridge in a manner that is detectable by the printer controller so that the controller is adjusted automatically without the need for user intervention.
A further object of the invention is to provide an encoding system which can be configured for a wide variety of printer cartridge types.